Modulating the nonlinear absorption response of SnO_x thin films via phase engineering

Phase (composition) is known to play a key role in determining the electronic and optical properties of amorphous oxide semiconductors. In this work, modulating the ultrafast nonlinear optical (NLO) response of SnO 2 and SnO thin films by tuning oxygen partial pressure during film sputtering is explored. Femtosecond Z-scan results demonstrate that intermediate phases have no profound impact on the two-photon absorption (TPA) response of SnO 2 and SnO films. Interestingly, the magnitude of the effective nonlinear absorption coefficient ( β eff ) of both intermediate SnO 2-x and SnO x are enhanced after the change of Sn 2+ /Sn 4+ composition ratio, as measured by picosecond Z-scan technique. Femtosecond degenerate pump-probe measurements show that intermediate phases accelerate the carrier trapping and improve the defect-related carrier absorption in SnO x (SnO-rich) film, while intermediate phase suppress the TPA response of SnO 2-x (SnO 2 -rich) films, therefore carrier-induced absorption dominates the NLO behavior of SnO 2-x film on picosecond regime. Our results indicate a simple and effective way to modulate the NLO response of transparent conductive oxide SnO 2 and SnO.